1. Field of the Invention
The present invention relates to an apparatus and method for inspecting the appearance of tires. In particular, the invention relates to a tire appearance inspection apparatus and method in which tire appearance is inspected by performing an image processing on captured images of the appearance of a tire.
2. Description of the Related Art
A conventionally known tire appearance inspection apparatus captures images of the tire surface with an image capturing device and determines acceptance or rejection of the tire through an image processing on them by an image processing device, by which defects (defective spots) made in the tire building process are detected.
The image capturing device of a tire appearance inspection apparatus may consist of a rotating table for rotating a tire to be inspected, a plurality of illuminators for shining a slit light on the tire surface, such as the inside surface of the tire, and a plurality of cameras for capturing the images of the tire surface illuminated by the slit light. The illuminators may employ red laser, and the cameras used may be CCD area cameras. The images of the inside surface of the tire are thus captured using a technique called the light-section method. The captured images shot by the plurality of cameras and obtained as sectional shapes of the tire inside surface are outputted successively to an image processing device connected to the cameras. The image processing device produces an inspection image by combining the captured images of the tire inside surface for the whole circumference of the tire and performs necessary image processing on the inspection image. In this manner, the tire appearance inspection apparatus inspects the tire surface for defective spots, thereby determining acceptance or rejection of the tire. For example, the tire surface is inspected for the presence or absence of defects by checking changes in the gradient of luminance of pixels constituting the captured images or comparing height information present in the pixels against threshold values.
For a successful inspection of the inside surface of a tire, however, it is prerequisite that the inspection image is obtained in advance with high accuracy. If, for instance, a stationary camera captures the inside surface of a tire rotating with its center out of alignment with the rotation center of the rotating table, then the distance to the inside surface of the tire shot by the camera changes with the rotation of the tire. This will result in the captured images of the cross-sectional shapes having positional shifts, or differences, in the tire radial direction. Hence, it is necessary to align the captured images if an accurate inspection image is to be obtained.
As a way to align captured images, all the captured images may be aligned uniformly, using the captured image with the closest distance between the camera and the tire inside surface for reference. In this case, however, there may be cases where defects in the radial height of the tire, even if they exist, are also removed by the alignment. Otherwise, it may be possible that the trouble is taken to capture the images for the second time by repositioning the tire to align the rotation center of the rotating table with the tire center. But such a procedure is of course detrimental to inspection efficiency. Therefore, if the inspection efficiency is to be enhanced, it is considered necessary to automatically eliminate by image processing the effects of such eccentricity, or nonalignment of the rotation center of the rotating table with the tire center, when producing an inspection image from the captured images.
The present invention has been made to solve the above-described problem, and an object thereof is to provide a tire appearance inspection apparatus and method that utilizes image processing in accomplishing tire appearance inspections with high accuracy.